Reinforced concrete plate construction

ABSTRACT

A unitized framework of steel beams with reinforcing rods and stiffening brackets welded throughout, and made completely rigid by casting concrete within the framework and bonding the concrete to the framework, provides a rigid panel that approximates the characteristics of a reinforced concrete plate while requiring less concrete and less steel than prior art panels for equal load conditions. The steel and concrete plate is constructed by arranging steel members into a framework, the size and shape of the desired plate, and welding adjacent mitered ends of the members together. Added framework rigidity is provided by welding stiffening steel members at each corner. A plurality of reinforcing rods, spaced apart, extend from one side of the framework to the other. The reinforcing rods are first welded to a spacer bar having predetermined holes slightly larger than the rods and are then welded to the steel members. Added lateral support is provided for the reinforcing rods by welding several additional rods to the opposite sides of the framework substantially perpendicular to the first set of reinforcing rods. The rigid plate construction is finalized by casting concrete into the steel framework which is previously prepared with a bonding agent. The resulting unitary steel and concrete plate requires less concrete and less steel than normal panels when subjected to equal loads.

United States Patent 1 11 1 Kahn 1451 Nov. 27, 1973 REINFORCED CONCRETE PLATE CONSTRUCTION [76] Inventor: Burton M. Kahn, c/o Kahn Construction Co., 51 Gillett St., Hartford, Conn. 06105 22 Filed: Mar. 15, 1971 21 Appl.No.: 124,322

[52] US. Cl 52/125, 52/223, 52/225,

52/231 [51] Int. Cl. H E04c 3/26, E04c 5/08 [56] References Cited UNITED STATES PATENTS 2,234,663 3/1941 Anderegg 52/223 R 1,000,089 8/1911 Haas 249/97 3,049,775 8/1962 Ondeck 25/118 T 1,469,678 10/1923 Newell 52/601 1,912,290 5/1933 Marks 52/601 1,637,215 7/1927 Coppock 52/600 2,691,292 10/1954 Roberts 52/125 2,615,678 10/1952 Stent 52/223 R 2,921,463 1/1960 Goldfein 52/ 723 2,850,890 9/1958 Rubenstein 52/309 3,468,090 9/ 1969 Ll-Iermite... 52/724 3,397,494 8/1968 Waring 52/122 3,236,019 2/1966 Ballou 52/125 2,310,442 2/1943 Knudsen 52/600 1,031,926 7/1912 Hansbrough 52/ 259 FOREIGN PATENTS OR APPLICATIONS 3/1931 Switzerland 52/223 R 1,095,395 6/1955 France 52/223 R Primary ExaminerFrank L. Abbott Assistant Examiner-Leslie A. Braun Att0meyMattern, Ware & Davis [5 7] ABSTRACT A unitized framework of steel beams with reinforcing rods and stiffening brackets welded throughout, and made completely rigid by casting concrete within the framework and bonding the concrete to the framework, provides a rigid panel that approximates the characteristics of a reinforced concrete plate while requiring less concrete and less steel than prior art panels for equal load conditions. The steel and concrete plate is constructed by arranging steel members into a framework, the size and shape of the desired plate, and welding adjacent mitered ends of the members together. Added framework rigidity is provided by welding stiffening steel members at each corner. A plurality of reinforcing rods, spaced apart, extend from one side of the framework to the other. The reinforcing rods are first welded to a spacer bar having predetermined holes slightly larger than the rods and are then welded to the steel members. Added lateral support is provided for the reinforcing rods by welding several additional rods to the opposite sides of the framework substantially perpendicular to the first set of reinforcing rods. The rigid plate construction is finalized by casting concrete into the steel framework which is previously prepared with a bonding agent. The resulting unitary steel and concrete plate requires less concrete and less steel than normal panels when subjected to equal loads.

10 Claims, 8 Drawing Figures Patented Nov. 27, 1973 3,774,359

2 SheetsSheet 1 FIG. I 7' /7O INVENTOR. BURTON M. KAHN MATTERN WARE AND DAVIS ATTORNEYS Patented Nov. 27, 1973 2 Sheets-Sheet :5.

FIG. 5

6 mm Cu REINFORCED CONCRETE PIAATE CONSTRUCTION SUMMARY OF THE INVENTION This invention relates to reinforced concrete plates, and more particularly to steel framed reinforced concrete plates and methods for manufacturing them.

Although voluminous art has been developed in the building construction field, concrete and steel panels are still manufactured with all steel members in a simple or continuous span condition. The members are all semi-rigid and, consequently, are free to rotate and twist by themselves, retarded only by the concrete reinforcements. In order to strengthen the forces that these concrete panels can tolerate, large amounts of concrete are employed.

OBJECTS OF THE INVENTION It is a principal object of this invention to provide a steel and concrete panel which is a unitary rigid structure that approximates the characteristics of a reinforced concrete plate.

Another object of this invention is to provide a steel and concrete panel which is stronger and uses less concrete and steel than prior art panels.

Another object of this invention is to provide a steel and concrete panel of the above character which is applicable for use as walls, ceilings, and/or floors.

A further object of this invention is to provide a steel and concrete panel of the above character which, when mounted in place, equals or surpasses the characteristics of an embedded beam.

Other and more specific objects will be apparent from the features, elements, combinations, and operating procedures disclosed in the following detailed description and shown in the drawings.

The concrete and steel panel of this invention comprises a unitary welded steel framework with a network of welded reinforcing rods surroundingly reinforced by concrete. Resistance to twisting moments at the corners of the panel is established by welding stiffening members across each corner. The unitary nature of the panel is assured by bonding the steel framework to the concrete. Consequently, concrete shrinkage away from the steel framework is substantially reduced. The resulting panel which contains steel and concrete in intimate contact throughout, uses less concrete and steel than existing panels. The unitary rigid concrete and steel panel of this invention approximates the structural characteristics of a reinforced concrete plate. Such a construction far surpasses the normal prior art panel which at best is capable of withstanding the forces characteristic of beams.

THE DRAWINGS For a fuller understanding of the nature and objects of the invention, reference should be had to the following description taken in connection with the accompanying drawings, in which:

FIG. 1 is a top plan view of the concrete and steel panel of this invention, with one steel member in a straightening yoke;

FIG. 2 is a side view partially in cross section of one steel member of the panel of this invention prior to welding of the reinforcing rod.

FIG. 2A is a view similar to that of FIG. 2, with the reinforcing rod welded in place;

FIG. 3 is a side view partially in cross section of another embodiment of a steel member for the panel of this invention, prior to welding of the reinforcing rod;

FIG. 3A is a view similar to that of FIG. 3, with the reinforcing rod welded in place;

FIG. 4 is a perspective view of a removable pickup assembly mounted to a steel member of the panel of this invention;

FIG. 5 is a cross-sectional side view showing the panel of this invention installed in a completely embedded position; and

FIG. 6 is a schematic view showing the theoretical amount of reduction factor for simple span and embedded plates as a function of the physical constant of the panel.

DETAILED DESCRIPTION A concrete and steel panel 20 according to this invention can best be seen in FIG. 1. Panel 20 comprises an outer peripheral framework 21 of L-shaped (angle section) steel members 22, 24, 26 and 28. One end of steel member 22 and one end of steel member 24 are mitered and welded together to form a semi-rigid corner. The remaining corners of framework 21 are similarly mitered and welded. By welding the steel members together, the rigidity of peripheral framework 21 is increased along with its resistance to bending momerits.

Additional rigidity is provided to framework 21 by welding steel stiffeners 30 to adjacent steel members at each corner. The use of stiffeners 30 is included in the preferred embodiment since it substantially increases the frameworks resistance to bending moments. Furthermore, although angle section beams are shown in FIG. 1, it should be obvious to one skilled in the art that any steel beam, such as channel, I section etc., can be successively employed in carrying out the principles of this invention.

When steel members 22, 24, 26, and 28 are mitered and welded together along with the stiffening members 30, the steel members have a tendency to warp and twist. To prevent twisting and assure that each steel member is straight and in the desired angular relationship with the adjacent members, a straightening yoke assembly 70 is employed. Yoke assembly 70 comprises a straightening yoke 71 and adjustable bolts 72 and for steel 'members'24, 26 and 28 to assure that framework 21 is completelystraight and the desired angular relationship between the steel members is properly maintained. It should be obvious to one skilled in the art that clamps, turnbuckles and similar equipment can be employed in lieu of or with the bolts.

The next requirement in producing rigid concrete and steel plate 20 is to secure a network of reinforcing rods to framework 21. First, reinforcing rods 32 are placed in spacer bar 35 and then into spacer bar 37. Spacer bars 35 and 37 are shorter in length than the inside dimension of steel members 24 and 28, and contain a plurality of holes having a diameter slightly greater than the dimension of reinforcing bars 32. The holes in spacer bar 35 are located at a position that will assure that the central axis of each reinforcing bar 32 is substantially perfectly aligned with the center of gravity of steel member 24. As will be more fully explained below, the reinforcing bars 32 are welded to spacer bar 35 and then to steel member 24 substantially along its center line of gravity. The center line of gravity for each steel member is well known in the art, and generally refers to the line defining the center of gravity of individual cross-sections of said steel member.

In the preferred embodiment, the reinforcing bars 32 comprise deformed or notched peripheral surfaces. The use of deformed reinforcing bars presents a substantially greater surface area for holding interaction with the concrete. If desired, steel cables can be used in place of reinforcing bars 32. Reinforcing bars 32, after having been welded to steel member 24, lie within framework 21 in a limp, sagging condition. In order to straighten reinforcing rods 32 and assure that reinforcing rods 32 remain in a substantially straight condition, the reinforcing rods 32 are first circumferentially welded to spacer bar 37. The straightening operation can best be seen by referring to FIGS. 2 and 2A.

Steel member 28 comprises a vertically extending leg ter of gravity, reinforcing rods 32 will be welded to both legs 27 and 29.

To assure the substantial straightness and secure welding of reinforcing rods 32, the reinforcing rods are first cut, if necessary, to allow the terminating end of the reinforcing rods 32 to abut leg 27 of steel member 28 when the rods 32 have been straightened. Spacer bar 37 incorporates a plurality of bolts 41 which pass through cooperating holes in leg 27 of steel member 28. Nuts 43 are threaded onto bolts 41 and tightened against the outer edge of yoke 71 or leg 27.

In order to straighten reinforcing rods 32, the nuts 43 are rotated causing spacer bar 37 and reinforcing rods 32 to be drawn toward leg 27 of steel member 28. This process is continued until reinforcing rods 32 are substantially straight throughout their entire length.

As shown in FIG. 2A, the reinforcing rods 32, while maintained in their substantially straight position, are securely welded to steel member 28, with the central axis of the reinforcing rods 32 substantially aligned with the center line of gravity of steel member 28 on leg 27. The terminating ends of the reinforcing rods 32 are welded to leg 27 of member 28, and the portion of the reinforcing rods 32 that is in contact with leg 29 of member 28 are securely welded to member 29. The ends of rods 32 are similarly welded to members 24 and 28 to assure that rods 32 are securely welded and will remain in a substantially straight condition.

The straightening of reinforcing rods 32 and the welding of the rods along the centerline of gravity of the steel members are extremely important. The sub stantial straightness of rods 32 provide assurance that the panel of this invention when longitudinally tilted up or hoisted and placed in position will substantially possess the structural characteristics of a column. The welding of the rods at the centerline of gravity of the steel members provides assurance that any deflection of the panel of this invention causes the compressive forces generated to pull the steel members at their center of gravity, thereby preventing rotation of the steel members.

In FIGS. 3 and 3A, the welding operation of reinforcing rods 32 to a steel member having a centerline of gravity substantially above the intersecting legs of the bracket can best be seen. Steel member 60 comprises a vertically extending leg 61 which is substantially greater in length than horizontally extending leg 62. Consequently, the centerline of gravity on leg 61 is at a point substantially above leg 62. Although steel member 60 depicts an angle member, it is obvious to one skilled in the art that steel members, such as channel, I section, etc., would have the higher centerline of gravity depicted by member 60.

A plurality of holes would be drilled on leg 61 of member 60 having a diameter slightly larger than the diameter of reinforcing rods 32 at an axis coinciding with the centerline of gravity of member 60. Spacer bars similar tothe above-described spacer bars 35 and 37 are employed. However, the holes through which reinforcing rods 32 pass are juxtaposed to the holes in leg 61 and are substantially aligned therewith. Once reinforcing rods 32 have been securely welded to one end of steel and concrete plate 20, rods 32 would be straightened, using the spacer bar and the cooperating bolts and nuts as described above. The only difference in straightening and welding rods 32 when using member 60 is that the rods 32 are not out prior to straightening, and, instead, advance through the hole in leg 61 during the straightening operation.

After rods 32 have been substantially straightened, rods 32 are circumferentially secured to the inside face of leg 61 of member 60 by weld 65, best seen in FIG. 3. The portion of rods 32 which extend beyond the outside face of leg 61 of member 60 are burned off and then secured to the outside face of leg 61 by plug weld 64, best seen in FIG. 3A.

It is important to note that members 24 and 28 must be straightened after each welding operation as previously described for member 22 using yoke assembly 70. The straightening operation on the steel members must be performed for each steel member after every welding operation on that member to assure and maintain the member substantially straight and in the desired angular relationship with its adjacent members.

The next step in the construction of steel and concrete panel 20 is to place reinforcing rods 34 substantially perpendicular to reinforcing rods 32 extending from steel member 22 to steel member 26. Reinforcing rods 34 are welded at their ends to steel members 22 and 26, while also being welded to reinforcing rods 32 at each point of contact. After straightening steel members 22 and 26 with yoke assembly 70, the semi-rigid framework is moved to the casting bed. At this point in the construction of the panel, the semi-rigid framework is capable of being a beam by itself. However, all members are free to individually rotate and twist, since they are merely in a simple span condition.

The final step required to construct rigid panel 20 is to cast concrete 36 within the confines of framework 21. Prior to pouring of the concrete into framework 21, the entire interior steel framework is thoroughly cleaned to remove all scale, rust, etc. Various methods may be employed to clean steel framework 21, such as sand blasting, wire brushing, or pickling.

After steel framework 21 is clean and dry, a commercial bonding agent, which will create a bond between concrete and steel, is brushed, rolled, or sprayed onto the inside legs of steel members 22, 24, 26 and 28, along with spacer bars 35 and 37. After the required time has elapsed with epoxy applied to become tacky, concrete 36 is cast within the confines of framework The use of epoxy on steel framework 21 prior to casting of concrete 36, provides assurance that steel and concrete will bond together. Inprior art steel frame concrete panels, no provision was made for the shrinkage of the concrete. As a result, the steel members were free to deflect under load prior to contacting the concrete reinforcement. By placing a bonding agent onto cleaned steel members prior to casting of the concrete, concrete shrinkage is substantially eliminated and thereby gaps between the concrete and the steel are prevented. The resulting effect is the creation of a unitary steel and concrete panel which possesses the structural characteristics of a concrete plate.

Concrete and steel panel is now a completely rigid utilized structure which approximates the characteristics of an embedded beam. Regardless of whether or not a beam is in a fixed position, the beam bends under load, either dead or live. Consequently, a deflection occurs. In panel 20, in order for a deflection to exist, two

sides must move towards each other. Therefore, if

beams 22 and 26 are put in tension, they would tend to pull beams 24 and 28 together. However, movement of beams 24 and 28 towards each other places concrete 36 in compression. Since the entire panel 20 is rigidly unified, the major moment generated by these forces is at the corners of panel 20. Since each corner contains a stiffening bracket, the forces generated are resisted and the midpoint of beams 22 and 26 have less deflection than the exact midpoint of the panel.

Since the unitized steel and concrete panel 20 substantially reduces deflection, the panels resistance to moment is substantially increased and consequentily a thinner concrete slab is required while providing a panel of greater strength. Furthermore, it has been found that the steel and concrete panel of this invention may be lifted within two or three days after it has been cast. To assure bonding between the concrete and steel, members 24 and 28 are straightened and a slight tension is placed on 32. As the concrete sets and starts to shrink, the tension is reduced.

If beams 22 and 26 were substantially greater in length than beams 24 and 28, an additional stiffening and attachment rod 80 would be welded to the steel members substantially at their midpoint. This type of reinforcing rod provides the added stiffness required to allow all components to act together, while also providing an additional surface to which interior panels may be welded.

In FIGS. 1 and 4, removable pickup unit 38 can best be seen. In the preferred embodiment, two pickup units 38 are fixed to the outside surface of vertically extending leg 27 of steel member 28 in positions equidistant from each other and from the ends of member 28. If desired, pickup unit 38 can be secured to any or all of the steel members forming framework 21.

Pickup unit 38 comprises a substantially Ushaped bracket 66 comprising a pair of holes through which bolt 67 passes and is retained by nut 68.

The back plate 69 of bracket 66 is bolted to leg 27 of member 28, and incorporates a hole for cooperative association with bolt 41 with spacer bar 37. With pickup unit 38 securely bolted to leg 27 of steel member 28 and the steel and concrete panel 20 completely cast, as will be described below, units 38 can be used to tilt up or lift the entire panel 20. Hoisting rope is looped around bolt 67 and secured to a lifting crane well known in the art. Since no tie or knot is required in connecting to pickup unit 38, panel 20 can be easily lifted without requiring adjustment for relieving slack in the hoisting rope. As the panel is lifted, the hoisting rope is free to rotate about bolt 67, thereby maintaining a constant tension, slack free hoisting line. After the panel is in the desired position, pickup unit 38 is removed.

Concrete and steel panel 20 approximates the characteristics of an embedded beam, but cannot achieve complete embedment until securely mounted in position. In FIG. 5, panel 20 is shown mounted in position as a floor member. Structural I beams 44 are mounted to supporting base 42 and panels 20 are mounted to beams 44.

Steel beams Y22 and 26 are welded along their entire length to I beams 44. At all positions, except along the outer periphery of the floor being constructed, steel beams 22 and 26 and steel beams 24 and 28 (not shown) will be adjacent to each other. At each of these positions, steel beams 22 and 26 and beams 24 and 28 are welded to each other as well as to I beam 44. This interwelded construction leaves the steel beams forming the outer periphery of the floor as the only areas where a completely rigid structure has been established. In order to attain the characteristics of an embedded beam, triangular stiflening wedges 46 are welded to the steel beams forming the outer periphery of the floor and to I beam 44.

With the entire peripheral framework 21 of each panel 20 securely welded to the framework of an adjacent panel or stiftening wedges 46, the end of each individual panel as well as the entire floor structure cannot rotate. As a result, each panel 20 is converted into a double cantilevered beam, with all loads on the panels being converted in part to tensile stresses which are easily accommodated by reinforcing rods 32 and 34. Experimentation has shown that a weight reduction of about 40 percent canbe achieved in manufacturing floor panels with strength that is equal or substantially greater than existing floor panels.

It is well known in the art that the maximum deflection at the center of a simple beam is equal to WI 8 for a usiraamyai'ssisutsd load. When the beam is fixed at ous parameters. The simplified equations for the maximum moment at the specified location under a uniformly distributed load are as follows:

Simple Span at midpoint: M W1 /8 (\IJOM Embedded or Fixed:

At ends: M=w 1 /12 111 14 At midpoints: M wl /24 (41 m 'u is determined from the calculation of complex hyperbolic differential equations and is dependent upon many varying parameters. These parameters include the modulus of elasticity of steel and concrete, the moment of inertia of the plate, the size and type of steel members, concrete and its functions, Poissons ratio, span, width, effective thickness of the panel, and the load placed on the panel.

In FIG. 6, the theoretical moment reduction factor k is plotted as a function of u for each of the above enumerated equations where (41) u is a solution to the complex hyperbolic differential equations based upon the above-enumerated parameters.

By referring to FIG. 6, the theoretical reduction in the bending moment of the panels of this invention can be determined. By producing the concrete and steel panel of this invention with a u factor equal to three, which would be common, the maximum moment at the midpoint of the panel would be 50 percent less than normal concrete beams. The substantial moment reduction in the concrete and steel panel of this invention is achieved by the complete unitary construction of the steel and concrete. By having a panel constructed so that it is substantially a unitary plate, the advantages of steel and the advantages of concrete can be incorporated to provide a new, improved panel with optimum characteristics.

Although the panels discussed above have been rectangular in shape with exposed surfaces of concrete, it should be obvious to one skilled in the art that the panels can be manufactured in any size of shape such as curved panels for bins, silos, or domes. Furthermore, the panels can be manufactured with many decorative surfaces by bonding stones, sand finishes, or other such materials to the concrete. The steel edge can also be decoratively changed by calking or placing bricks or stones along the outer panel. Furthermore, by varying the spacing of the reinforcing rods or eliminating reinforcing rods in certain areas and incorporating stiffening members, finished panels can be manufactured with suitably sized openings for windows or doors. Furthermore, the panels of this invention can be used as concrete forms or inside and outside wall forms, whereby concrete can be cast inside a preset gap between two panels.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efiiciently attained and, since certain changes may be made without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative so as to obtain the benefits of all equivalents to which the invention is entitled.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter and desire to secure by Letters Patent is:

I. A unitary reinforced panel comprising: A. a peripheral closed framework of welded members of relatively high tensile strength forming a unitary integral unit of polygonal configuration; B. a reinforcing network incorporating:

a. a plurality of substantially straight load carrying reinforcing members of relatively high tensile strength extending across said closed framework in parallel spaced relationship interconnecting at least two pairs of opposed ones of said framework members, and b. said reinforcing members 1. individually welded to said framework members at substantially the center of gravity of the cross-section of the framework member, and

2. individually welded to each other at every cross-over contact location;

C. material cast about said reinforcing network and substantially in contact with said framework; and

D. stiffening members embedded in said cast material diagonally extending between adjacent-framework members near the comers of said framework and welded to said framework members.

2. A reinforced panel as defined in claim 1, wherein said framework, said reinforcing, and said stiffening members are steel.

3. A reinforced panel as defined in claim 1, wherein said frame members and said stiffening members are substantially straight.

4. A reinforced panel as defined in Claim 3, wherein said material is concrete.

5. A reinforced panel as defined in claim 1, wherein said casting material comprises material of relatively high compression and relatively low tensile strength.

6. A reinforced panel as defined in claim 1, wherein said framework is substantially cleaned and free of rust, dirt and scale.

7. A reinforced panel as defined in claim 6, and a bonding agent between the framework members and said cast material, capable of substantially intimately connecting said framework members with said cast material.

8. A reinforced panel as defined in claim 1, wherein pickup assemblies are removably mounted to the outer surface of at least one framework member equidistant from the ends thereof and from each other.

9. A reinforced panel as defined in claim 8, wherein said removable pickup assemblies are further defined as comprising a bracket adapted for cooperation with a hoisting bolt which is maintained in parallel spaced relationship to said framework member.

10. A reinforced panel as defined in claim 1, further comprising a stiffening member of relatively high tensile strength longitudinally spanning between the midpoints of two opposed ones of said framework members and adapted for interconnection with adjacent panels. I. t 

1. A unitary reinforced panel comprising: A. a peripheral closed framework of welded members of relatively high tensile strength forming a unitary integral unit of polygonal configuration; B. a reinforcing network incorporating: a. a plurality of substantially straight load carrying reinforcing members of relatively high tensile strength extending across said closed framework in parallel spaced relationship interconnecting at least two pairs of opposed ones of said framework members, and b. said reinforcing members
 1. individually welded to said framework members at substantially the center of gravity of the cross-section of the framework member, and
 2. individually welded to each other at every cross-over contact location; C. material cast about said reinforcing network and substantially in contact with said framework; and D. stiffening members embedded in said cast material diagonally extending between adjacent framework members near the corners of said framework and welded to said framework members.
 2. A reinforced panel as defined in claim 1, wherein said framework, said reinforcing, and said stiffening members are steel.
 2. individually welded to each other at every cross-over contact location; C. material cast about said reinforcing network and substantially in contact with said framework; and D. stiffening members embedded in said cast material diagonally extending between adjacent framework members near the corners of said framework and welded to said framework members.
 3. A reinforced panel as defined in claim 1, wherein said frame members and said stiffening members are substantially straight.
 4. A reinforced panel as defined in Claim 3, wherein said material is concrete.
 5. A reinforced panel as defined in claim 1, wherein said casting material comprises material of relatively high compression and relatively low tensile strength.
 6. A reinforced panel as defined in claim 1, wherein said framework is substantially cleaned and free of rust, dirt and scale.
 7. A reinforced panel as defined in claim 6, and a bonding agent between the framework members and said cast material, capable of substantially intimately connecting said framework members with said cast material.
 8. A reinforced panel as defined in claim 1, wherein pickup assemblies are removably mounted to the outer surface of At least one framework member equidistant from the ends thereof and from each other.
 9. A reinforced panel as defined in claim 8, wherein said removable pickup assemblies are further defined as comprising a bracket adapted for cooperation with a hoisting bolt which is maintained in parallel spaced relationship to said framework member.
 10. A reinforced panel as defined in claim 1, further comprising a stiffening member of relatively high tensile strength longitudinally spanning between the midpoints of two opposed ones of said framework members and adapted for interconnection with adjacent panels. 